The present invention relates generally to a test fixture for printed circuit boards. More specifically, the present invention relates to a test fixture for the automatic testing of printed circuit boards which includes an air-tight self-sealing system.
In the field of automatic testing equipment (ATE), it has been well known to employ a vacuum actuated test fixture for receiving electronic circuit devices to be tested and then electrically interconnecting the electronic circuit devices to the automatic testing equipment. In the prior art, it has become well known for the automatic testing equipment to include a plate, commonly referred to as a probe plate, for carrying an array of test probes. Also, a board is provided for carrying the electronic circuit device to be tested, commonly referred to a diaphragm board. The diaphragm board is typically positioned above and in spring-biased relation to the probe plate. As a result, a chamber is formed between the probe plate and the diaphragm board. To actuate the diaphragm board into contact with the test probes present on the probe plate for testing, air in the chamber is evacuated to create a vacuum therein. As a result, the diaphragm board is drawn toward the probe plate for testing of the electronic circuit device. The vacuum is maintained by a seal system present between the diaphragm board, probe plate and the electronic circuit board to be tested.
For example, U.S. Pat. No. 4,799,006, issued to Strohschneider, incorporated herein by reference, discloses a test fixture with a self-sealing vacuum skirt to ensure that the vacuum developed in the chamber between the diaphragm board and the probe plate is maintained to enable the electronic circuit device to dwell at the test probes in the probe plate for testing. In addition, U.S. Pat. No. 5,200,694, issued to Nesbitt et al., incorporated herein by reference, discloses a head assembly for a printed circuit board test fixture which includes another example of an attempt in the prior art to provide a seal for the chamber between the probe plate and the diaphragm board.
The prior art test fixtures for printed circuit boards typically include a vacuum-tight resilient member positioned between the lower probe plate and the movable diaphragm board which carries the electronic circuit device to be tested. Various structures have been attempted to achieve a quality seal, such as collapsible skirts and double seals which sit atop one another. Each of these attempts in the prior art suffer disadvantages in the way of cost of assembly, ease of assembly, ease of use, cost of maintenance and repair, and overall seal quality. For example, test fixtures which employ only one seal are inadequate because if that seal fails, a vacuum cannot be maintained. Complex seal member construction is also undesirable because the cost for materials and assembly is high. For example, an elaborate seal construction will typically require each corner of the test fixture to be mitered and glued thus increasing manufacturing costs. Seal arrangements, which require custom extruded components, are also disadvantageous. Further, test fixtures in the prior art, which employ two seals, are inadequate because they are integrated together requiring replacement of both seals even if only one seal fails.
Due to the demand for a test fixture which can create a quality seal at low cost, it is desirable for a test fixture to include two separate seal members which employ standard stock material which can be easily replaced upon wear or failure. It is also desirable to include a dual seal system where one seal may compensate for inadequacies in the other seal to ensure a complete and quality seal at each test cycle. It is desirable that no custom extruded parts or mitered and glued corners be required.